Most electric or electronic devices are operated with electrical power taken from the public electricity grid (shortly called “grid” or “mains” in the following). As the grids of different countries provide different AC voltages, for example about 115 V in the USA and about 230 V in Europe, provisions have to be taken that allow the adaptation of a device to such different voltage supplies. From the EP-0531995 A2, a circuit is for example known in which the user has to close or open a switch depending on the grid the associated apparatus shall be connected to. This is not convenient but prone to erroneous operation.